THE PERIO RESTORATIVE INTERFACE
Its role in long term aesthetic stability
Dr Derry Rogers
The interface between the gingival margin and osseous crest is the most important area in terms of long term gingival stability. Its all about the position of the restorative margins relative to the osseous, not just referenced to the free gingival margin (FGM).
10 yr Veneers..stable tissue margins!
8 year Crowns..recession!
The aesthetic demands of our patients often require us to place restorative margins subgingivally to hide dark tooth bases. So we are faced with the decision of subgingival, equigingival or subgingival margins and how to manage them. If margins are placed too close to the osseous crest, a chronic inflammatory response will be created with resultant gingival inflammation (fig 1). Placed too far away from the osseous crest with an adjacent deep but healthy gingival pocket, recession is a significant risk if the manipulation of the friable gingivae is excessive (fig 2).
The key to long term gingival stability is to know the position of the osseous crest relative to the healthy FGM. With this knowledge, we can then decide on the placement position of the restorative margin. The closest the osseous can be to the restorative margin is 2.5 mm, otherwise a biological width invasion will be created. The different positions for restorative margin positions include:
1: Normal Gingival sulcus
With an osseous to FGM distance of 3mm, we can place the restorative margin no closer than 2.5 mm to osseous, thus .5mm sub-gingival.
This can be achieved by prepping to the restorative margin, placing a Number “00” Gingival retraction cord (which will provide .5mm retraction) and re-prepping to the newly retracted FGM. The restorative margin will now reside 2.5mm from the osseous crest. This may be required where the tooth color is darker and requires hiding from the aesthetic eye. The subgingival margin demands perfect provisionals to avoid plaque retention in order to protect the tissue until cementation of the final restoration.
2: Normal gingival depth with high osseous
There are occasions where the probable gingival sulcus is 3mm but the probed osseous is greater than 3mm from the FGM. This is representative of a long junctional epithelium and indicates a high osseous position such as a fenestration or minimal buccal bone in post orthodontic treatment in the canine region . The clinician needs to be very careful with the gingival manipulation, as recession is a potential long-term risk. Placement of retraction cord must be non traumatic to protect the hemidesmosomal attachments. (Note the high osseous level above 13 that is a risk zone for gingival retraction)
3: Deep gingival sulcus
There will be occasions where there is a deeper gingival sulcus than 3mm and we need to decide where to place the restorative margin, equigingival or subgingival in order to maintain aesthetics especially in the situation of a dark rooted tooth to be prepped.
Our reference is restorative margins no closer than 2.5 mm to the osseous crest. The gingival margin may migrate with recession in the event of being handled too traumatically (such as cord placement) where the placement instrument damages the long junctional epithelium. Again, the deeper the subgingival preparation for colour management, the greater the accuracy of the provisional margins.
LONG TERM STABILITY
The ability to deliver long-term gingival complex stability depends upon referencing the FGM to the osseous crest. This requires being able to probe the osseous crest under LA prior to commencing the preparation. The clincian needs to be mindful of the root tapering to the apex when initiating osseous probing. The periodontal probe needs to enter the gingival sulcus, angled away from the vertical towards the apex, then pushed through the junctional epithelium and finishing at the osseous shelf.
We cannot violate the 2.5mm separation zone otherwise there will be a “biological width invasion” with resultant chronic gingivitis. (Note the interproximal area of chronic erythema indicating the interproximal biological invasion)
Fig 6 Subgingival prep required
Fig 7 Osseous dictates prep depth
The correct positioning of the restorative margin relative to a healthy gingival margin and to the osseous, will provide us with long term gingival health and aesthetic success. Remember to reference the osseous on your preps prior to final margin refinement and preferably prior to the commencement of your preparations.
Delivering excellent provisionals is key to maintaining gingival health so that at insertion gingival irritation and bleeding is kept to a minimum.